One of the problems we must deal with when considering the threats of war and likely responses is the effectiveness of any weapons used and the tools to prevent them from working. This is almost impossible to determine given the secrecy militaries must maintain.
For example, how effective is any US missile shield? Should a hostile nation such as North Korea launch five missiles at the US, can we knock them down? Of course, given the reliability of North Korean missiles, the things might just blow up on the launch pad. But assuming your enemies' weapons will malfunction is a poor excuse for a defense.
Anyway, there are other nations whose weapons one would be foolish to assume are duds or otherwise cannot make the trip to their intended targets. Since these weapons are unlikely to be armed with conventional weapons, this is a serious issue. And one that must keep military planners constantly busy.
More on page two.